What Causes Patches Of Hair Loss In Chihuahuas?

This is a common occurrence in small Chihuahuas.  Around 4 months they can begin to "grow out" of their puppy fur.  I would still have the vet take a look to make sure there is no mange or mites.  If that is negative I would not worry.  As long as the skin looks healthy underneath with no redness or scaling - they are probably just growing in new fur.  This happened to my Chi from 12 weeks to 5 months.  At first it was the hair on his front legs - then on his sides and upper hips.  My vet took a scraping and it came back negative for any problems.  Now his fur is back and beautiful!

My chihuahua is 3 years old and she is losing her hair in different places like on her head, thighs, and on her sides. I have taken her to two different vets and they did a skin scrape and blood test and can't figure out whats wrong. She also keeps biting the bottoms of her feet. I have not spade her yet, could that have something to do with this?

It could be the food your giving the dog, it might not have enough vitamins. Chihuahuas are very active dogs they need a little extra vitamins in their lil body. Good Luck :)

Stress or Trauma is very common due to the nervous and timid nature of the breed.

  Yes, she should see a vet. She needs a skin scraping for mange mites. One type of mange can kill a pup if not treated and the other still needs to be treated.  She can also get vaccinated and rabies shot. Spaying will probably have to wait. Too bad it couldn't be just a to tight sweater. Hope all works out. She is not a happy puppy.  

Possibly mange

Is she supposed to be a hairless Chuchuahua?  If not, take her to a vet!  Something is obviously wrong with her.